A canister of this type is described in the document EP-A-0.026.691, in the name of the applicant.
The preservation of numerous products and biological specimens, particularly in the form of thin closed tubes called "specimen holders", of a usual capacity varying between 0.25 and 0.5 cm.sup.3, is effected by immersing these holders in insulated receptacles, typically double walled, filled with a cryogenic liquid, typically liquid nitrogen. These receptacles have a capacity which can vary from 1 liter to more than 1000 liters and contain a variable number of holders, from about fifty to more than a million. The holders are not introduced in bulk into the receptacles but are grouped in intermediate containers called "canisters", according to the present invention, which can contain a number of holders varying from 50 to about 2000, according to the dimensions of the holders and the canisters.
When a canister, first loaded with specimen holders, is introduced into a receptacle filled with cryogenic liquefied gas, this latter penetrates the canister through its lower perforated end and can, if the canister is rapidly immersed in the liquid, lead to a substantial raising of the specimens relative to the canister with the risk of their leaving the canister by the upper end and being dispersed in the liquid in the receptacle. Moreover, it is desirable to emplace rapidly the canister in the bath of liquefied gas to avoid losses of cold and excessive vaporization of this latter.